The aim of this study was to determine the period prior to interference and the total period of prevention against interference of weeds in sunflower (hybrid M 734). The experiment was arranged in a complete randomized block design, with four replications. The treatments consisted of plots constituted by periods of control and presence of weeds. For the control periods, the sunflower plants were kept wedd free during increasing periods of 7, 14, 21, 28, 35, 42, 49 and 125 days after emergence (DAE). During cohabitation, the sunflower culture was maintained in the presence of the weed community during the same periods. Total density and dry weight of the weeds and plant height, chapter diameter, seed yield and oil of the sunflower plants were evaluated. For seed yield, the period before interference was 15 DAE of the culture, and the total period of prevention against weed interference was 39 DAE. The critical period of weed interference covered 24 days of the sunflower cycle. As for oil yield, the period before interference was 32 DAE, while the total period of prevention against weed interference was 28 DAE.
weed competition; Helianthus annuus; weeds
